Automated clutches are increasingly used in motor vehicles, just as automated gears, not only for improvement in comfort, but also due to the resultant possible reduction of consumption. Conventional clutches contain a plate spring that keeps the clutch in the engaged state. The clutch must be disengaged with an actuation device against the force of the plate spring. It is especially due to the use of precisely controllable electric motors that it has recently become possible to eliminate the powerful plate spring that closes the clutch by pressure and to close the clutch by pressure with the help of the external actuation device. In that way, the clutch can be made in a lightweight fashion. Weak opening springs can be contained in it so that the clutch will reliably open completely.
Electric motor actuation devices for automated clutches frequently contain a spindle drive in which the rotation of a spindle, driven by the electric motor, is converted into a movement of an actuation member for the clutch. The rotation of the spindle is acquired by an incremental sensor, which, depending on a predetermined angle of rotation, produces a pulse that is counted in a control unit. The position of the actuation member must be known absolutely for the sake of the precise control of the clutch; therefore, the actuation device must be adjusted as required, that is to say, the counting status of the incremental sensor must be associated with a predetermined position of the actuation member. This is done in an actuation device according to DE 443 38 25 C2 in the following manner: As a result of the drive provided by the electric motor, stops are approached where one corresponds to the fully opened position of the clutch, while the other one corresponds to the fully closed position. The fact that the stop has been reached is sensed on each occasion so that the currently existing counting status of the pulses of the incremental sensor can be taken as a standard or reference status.